Units Definition and 998 Threads

English units are the units of measurement used in England up to 1826 (when they were replaced by Imperial units), which evolved as a combination of the Anglo-Saxon and Roman systems of units. Various standards have applied to English units at different times, in different places, and for different applications.
The two main sets of English units were the Winchester Units, used from 1495 to 1587, as affirmed by King Henry VII, and the Exchequer Standards, in use from 1588 to 1825, as defined by Queen Elizabeth I.The English units were replaced by Imperial Units in 1824 (effective 1 January 1826) by a Weights and Measures Act, which retained many though not all of the unit names and redefined (standardised) many of the definitions.
Use of the term "English units" can be ambiguous, as, in addition to the meaning used in this article, it is sometimes used to refer to United States customary units, which have somewhat different definitions, or to Imperial units, the standard units throughout the British Empire and Commonwealth.

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  1. B

    Euler Bernoulli Beam 4th order ODE -Balance of Units

    Folks, I am trying to understand the balance of units for this eqn ## \displaystyle \frac{d^2}{dx^2}(E(x)I(x) \frac{d^2 w(x)}{dx^2})+c_f(x)w(x)=q(x)## where ##E## is the modulus of Elasticity, ##I## is the second moment of area, ##c_f## is the elastic foundation modulus, ##w## is...
  2. A

    What are the units of a definite integral and its derivative?

    Hi, Suppose we have f(x) = x3. Integrating this function using the definite integral with the upper boundary being 3 and the lower boundary being 1 would result in 20. Does 20 have any units or is it unitless? Seeing how it is the area underneath a curve, I would imagine that it has square...
  3. D

    Why is the Exponential Constant e Unitless?

    Is there a reason why e doesn't have units attached? I've kind of just accepted it but was wondering the reason behind it.
  4. E

    Sofware to check equation units

    Hello everybody! Once again, someone searched elsewhere in September a project topic for her software class, and I suggested one in November , so this topic as well must be available to other people... A piece of software could check that the units of an equation fit together, like: a...
  5. P

    Energy Density Units Electromagnetic Waves

    Homework Statement In what units is energy density measured? 1. Watts 2. Watts per cubic meter 3. Newtons per meter 4. Joules per cubic meter Homework Equations E = cB (as derived by Maxwell) The Attempt at a Solution This question is so basic yet I'm confused. I thought...
  6. B

    The argument of the change of units

    Hello. I have a problem with the statement that specific values, like the speed of light, have no meaning because we can change these values by a change of units. For measures attached with units the value(number) has no meaning "per se", I'm ok with that. (Unlike pure numbers like ratios...
  7. I

    Calculating Velocity in a Venturi Effect Nozzle: Converting Units

    Homework Statement Venturi effect nozzle.. Starts off at 100cm and goes down to 40cm. The flow rate of the gas is 2.23 m3/s. What is the average velocity at the beginning and end of the nozzle. Homework Equations Continuity Formula, Bernelli = Q = A1V1=A2V2 The Attempt at a...
  8. S

    Units of slope in a tension vs θ (theta) graph

    Homework Statement In a physics lab we were finding slope on semi-log graph paper, with the y (up) axis representing tension in Newtons, and the x (sideways) axis representing θ in radians. Sadly, the prof introduced the new concept of natural logs to me - I'd never heard of these until this...
  9. N

    Understanding mA/mV and A/V Units in Transconductance Parameters

    Homework Statement Is mA/mV the same as A/V? Suppose I have 6.42mA/26mV the milli's cancel out and give A/V? This is in regards to transconductance parameters for transistors, but it's just a question of units.
  10. N

    Stress problem, units? (some calculation inside)

    Homework Statement The stress of a particular material, σ, is a function of x and y, where x is stress in the x-direction and y is stress in the y direction. the stress function is given by: σ(x,y)= e^{y} ln(2x+3y) when x=2cm @ 3cm/s y=3cm @ 1cm/s Homework Equations...
  11. S

    Kinematics - getting different answers when using different units

    Homework Statement A jetliner touches down at 270 km/h. The plane then decelerates (i.e., undergoes acceleration directed opposite its velocity) at 4.5 m/s2. What’s the minimum runway length on which this aircraft can land? Homework Equations v2fx = v2ix + 2axΔx The Attempt at a Solution i...
  12. T

    Appropriate units for temp problem

    Homework Statement (T-T envir)/(T int - T envir) = exp (-(2h/pcL)t) T = temp (°C) h = heat transfer p = density (kg/m^3) c = specific heat (J/Kg * K) L = plate thickness (m) t = Time (s) What are the appropriate units for h? Show all steps... (equation is homogenous in units) The Attempt at...
  13. B

    How Do You Calculate the Oscillation Frequency of a Compressed Rubber Pad?

    So, I'm trying to brush up on my undergrad physics, and I'm sure this is a bone-headed question, so please bear with me. Homework Statement A heavy object, when placed on a rubber pad that is to be used as a shock absorber, compresses the pad by 1cm. If the object is given a vertical tap, it...
  14. B

    What is the Unit of ω=sqrt(g/x0) and How is it Converted to Radians?

    So, I'm trying to brush up on my undergrad physics, and I'm sure this is a bone-headed question, so please bear with me. Homework Statement A heavy object, when placed on a rubber pad that is to be used as a shock absorber, compresses the pad by 1cm. If the object is given a vertical tap, it...
  15. M

    Understanding Units of Work in Physics: A Brief Explanation

    Hey there, I'm in a math class and we're covering some applications to physics and although I completely understand the math behind it and am getting the correct answers, I'm a little iffy on how some of the units work. Would anyone be kind enough to tell me whether or not my thought process...
  16. S

    Losing the Units: Explaining Why Exponentials are Dimensionless

    Hi All and sorry if this is too easy a question but here goes... Sines, Cosines and the rest of the trig functions are the ratio of two lengths and thus are dimensionless quantities. That is if I plug in a value for t in sin(ωt) there are no units. For example the solution of x'' +...
  17. P

    Need help simplifying units of slope for an angular acceleration vs torque graph

    In a lab we conducted in class we graphed angular acceleration vs torque, and found a positive linear correlation-easy enough. However I am getting rather stuck in simplifying the units of slope in terms of Kg, m, and s... I am fairly sure this will give me that angular acceleration equals...
  18. C

    Represent combinations of units in SI form

    Homework Statement Represent the following combination of units in the correct SI form using the appropriate prefix km*mN Homework Equations k = 10^3 m = 10^-3 The Attempt at a Solution km * mN = (10^3)m * (10^-3)N = m*N = Nm Have I done this correctly?
  19. R

    Confusion with units for Power Required Formula

    Hi all, I'm having trouble with the power required formula for steady level flight. Here's the formula: Preq = 4/3*W*sqrt(W/S*2/ρ*sqrt(3*CD0/(π*ε*A))) I'm using this for a small indoor RC fixed wing. The values I'm using are as follows: Weight, W = 0.3924N Wing Area, S = 0.073 m^2 Density, ρ...
  20. F

    What are the units for spectral energy density according to the Planck Law?

    I will just paste the link, cause its faster this way: http://scienceworld.wolfram.com/physics/PlanckLaw.html The last equation for spectral energy density if you look at the units you get eVs/m^3 or Js/m^3, yet energy density is supposed to be J/m^3. What am I missing here?
  21. P

    Medical Is blood donation actually valuable? Are all units really used?

    I donated blood at the Red Cross yesterday, and now I'm wondering about some of the claims they make, and whether it's really worth my time to donate. They say that you save a life every time you donate blood, and that all units donated are used. I don't see how this is possible. Surely...
  22. J

    Do some scientists create equation that arent based on si units.

    The base units are meters kg and seconds, right? So are some equations meant to use a different set, like cm kg minutes or something. And is it always assumed to be si unless told otherwise?
  23. J

    So what units should i use with E=mc^2?

    I guess this is a question about what units to use in any equation. Which ones pair together. If you use 300,000,000 m/s and 1 gram in e=mc^2, you will get 300,000,000, but what unit? Joules? How do you know which to use and which ones pair together?
  24. B

    Particle moving in electromagnetic field - converting units

    Homework Statement Show that the force on a moving charged particle F = qv × B from a magnetic field pointing perpendicular to the velocity produces a centripetal force and that this is equivalent to the equation pc = ABρ, where B is the magnetic field strength (in Tesla) and ρ is the radius of...
  25. 1

    Torque to linear force conversion and units

    I always get my foot-lbs and inch lbs confused and don't know if I am applying the correct unit. If I wanted to know how much linear force I can create from a given amount of torque I apply to a thread, I know that I need to find the mechanical advantage of the thread and the torque applied. I...
  26. C

    How Do I Resolve the Units in This Black Hole Mass Equation?

    Please bare with me, I'm not sure how to put in the maths on a forum like this. Ok so i was asked to combine two equations to get a third, this I have done. The equation is M = v squared x r and then the producet of those divided by G. M is the mass of a black hole v squared is the...
  27. A

    How are units combined/cancelled in this simple equation?

    The numerical answer is easy to find, but I'm wondering which units are in the answer and how those units are determined. Thanks in advance. (6.63E-34 J×s)(7.09E14 s) - 2.17E-19 J =
  28. Q

    Units of Wave Function: Joules or Vary?

    Do the units of a wave function vary? i have heard that it just joules. What do you think?
  29. F

    Measuring SI Units on a Desert Island

    A few years ago, I was reading about a contest open to everyone. The question was something like : if you were on a desert island, with unlimited natural resources, and access to a book with the most accurate values of properties for various natural things (i.e. gravitational acceleration on...
  30. S

    Converting Between CGS and SI Units in Electromagnetism: A Complete Guide

    So I understand that converting between CGS and SI units is no easy task when you look at the general form of each equation in electromagnetism, as you can't simply relate the two systems given they have different ways of looking at what is a derived unit and what is fundamental. But once you've...
  31. S

    Ansys Guru Needed: Troubleshooting Offshore Wind Turbine Tower Units

    Hi! I'm doing my master thesis about designing a offshore wind turbine tower for subarctic conditions and I have a major problem with units I'm not much familiarised with Ansys, so I use Ansa as preprocessor and launch the solve in Ansys The problem I have is in units. I'm using Ansys...
  32. V

    Magnetic Sensor Sensitivity units mV/V/gauss, etc.

    So I've been looking at magnetic sensor datasheets and I see the sensitivity is usually listed in units of mV/V/gauss. What does this mean? Let's say I need to sense changes in a magnetic field that usually ranges from about 10 gauss ( 1 mT ) to about 130 gauss ( 13 mT ). And I need to be able...
  33. S

    Find units of transition dipole moment

    I have been trying to figure out which formula for the relationship between oscillator strength and transition dipole moment is correct. Wiki had the following formula: http://photonicswiki.org/index.php?title=Transition_Dipole_Moment f = 4.703 \times 10^{29} \bar{v} \mu^{2}_{ge}\,\...
  34. G

    Measuring Length, Area & Volume: Classical vs Quantum Physics

    I am talking about length area and volume. As I reason it out in my own mind area (and volume) is based on length and involves 2 random measurements of length that are combined (with multiplication as the device of convention - could any other function be used to work as well and as...
  35. B

    Characteristic energy units of primordial fluctuations if gaussian

    Characteristic energy "units" of primordial fluctuations if gaussian Correct me if wrong, but I think a purely gaussian distribution of the primordial fluctuations could be characterized by a certain unit of energy (which I'll express as mass). If so, then the observed fluctuations are...
  36. R

    Gas flow units MSCMD, KM^3 and SM^3x10

    Is kM3/d 1000 m^3 a day or a kilometre^3 a day? I know it should be little m but this is what is written on our gas measuring instrument Are the units kM3/day 1000 cubic metres per day, or a kilometre cubed per day eg 1000x1000x1000 m^3 = 1e9 Thanks
  37. M

    Solve Angular Acceleration for Blade Radius | Homework Help

    Homework Statement A fan blade is rotating with a constant angular acceleration of +12.0 rad/s2. At what point on the blade, as measured from the axis of rotation, does the magnitude of the tangential acceleration equal that of the acceleration due to gravity? Homework Equations...
  38. K

    Entropy and Heat Capacity have the same units. Connection? Redundancy?

    Given that heat capacity is a ratio of change of energy over change of temperature, while entropy is a change of energy over absolute temperature... I was wondering if there is any basis for the idea that energy will tend to flow from media having low heat capacity to media having high heat...
  39. A

    Upgrade Your AC System with Hybrid Condensing Units | AEC.us.com

    I just found a manufacturer that makes a hybrid condensing unit that is roughly the same size as a 5-ton air-cooled one for residential and small building purposes, but it claims to be able to facilitate a 30-ton system. The manufacturer says that it really beats the efficiency of an...
  40. A

    Why is Mixing Units in the Nernst Equation Considered Accurate?

    One thing that always puzzled me on the Nerst equation is that you may mix the units of concentration and pressure. This, however, seems to be rather arbitrary. How can using the units of mol/L and atm in the same equation result in accurate results? It seems to be rather arbitrary...
  41. G

    Units of constant of proportionality, can I sum them like this ?

    Homework Statement Hello, I have four different, but known, dimensionless values C1, C2, C3 and C4 (they are actually contrasts that can be displayed on a crt monitor). I have measured the voltages (V1 and V2) required to produce C1 and C2 in isolation, but have had to measure V3 by combining...
  42. D

    Help filling in a formula correctly? Not sure about SI units etc

    Homework Statement It is estimated that a particular diffuse hydrogen cloud has a particle density of 3e7 cm^-3, and the temperature is 150 K. Calculate Jeans mass. Homework Equations Jeans mass is given by: (5kT/GmewM(H))^(3/2) . (3/4∏p)^(1/2) where k = boltzmanns constant =...
  43. I

    Unit Conversion: Astronomical Units, Parsecs and Light Years

    Hi everyone, It's been years since I solved a physics problem for school. Now that I'm back at it I could use some help on this problem: Question "The astonomical unit (AU) is defined as the mean centre to centre distance from Earth to the Sun, namely 1.496 x 10^11 m. The parsec is...
  44. D

    Converting to SI units w/ significant digits & scientific notation

    Hi. I'm asked to convert 2 year into the SI Unit seconds: Known: 1 Hr = 3600 s 1 Day = 86400 s So using a calculator... 1 yr = 365*86,400 = 31,536,000 I want to express the answer in scientific notation: Because the lesser number on has 3 significant digits, the scientific...
  45. L

    Converting equations in Natural units to SI?

    How can I convert an equation in units where hbar = c = 1 into an equation with hbar and c in SI units? I searched around a bit and wasn't able to find anything (I'm probably not asking the right question). Is there some general way to do it rather than just intuition from having seen the...
  46. M

    What are the units for inertia?

    Hello there, there have been a lot of conflicts between my physics teachers and university lecturers about the the units for intertia. Some say there aren't any units for inertia, and others say that it's in n/s. However, I don't know who to believe anymore... that's why I'm here :smile...
  47. P

    Solved: Dimensions of b/a in Pressure Equation

    Homework Statement Assuming that Pressure (P) of a particle is given by P = b - t^2 / ax where t = time, x = position Find the dimension of b/a. Homework Equations The Attempt at a Solution Using dimensional homogenity, I know that b represents time interval.
  48. H

    MHB What Are the Units in the Ring $\mathbb{Z}[\sqrt{-7}]$?

    I have to find the units in $\mathbb{Z}[\sqrt{-7}]$ so take $x,y\in\mathbb{Z}[\sqrt{-7}]$ then x has the form $a+b\sqrt{-7}$ and y has the form $c+d\sqrt{-7}$ for arbitrary x and y. If $(a+b\sqrt{-7})(c+d\sqrt{-7})=1$ then $(a-b\sqrt{-7})(c-d\sqrt{-7})=1$ and so...
  49. nukeman

    Simple Question: Units and volume of DNA - Can't get formula correct?

    Homework Statement Deoxyribonucleic acid (DNA) is thought to be the chemical compound responsible for the process of heredity. A sample of DNA was found to have density 1.10 g/cm3 and its molecular weight was estimated to be 3.04 × 108 g. What is the average volume occupied by one DNA...
  50. H

    MHB Finding the units in the ring F[x]

    I have to find all the units in the ring $F[x]$ where $F$ is a field. Clearly all polynomials of degree 0 are units as they are in the field F. Now suppose $\alpha(x)\beta(x)=1$ which gives $\mbox{deg}(\alpha(x))=-\mbox{deg}(\beta(x))$ which gives $\mbox{deg}(\beta(x)=\mbox{deg}(\alpha(x)=0$...
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